I really have no idea how this is going to end, but since the 'Plan' is to reset time, I can envision this:

After sending the kid into the future and causing a kind of reverse butterfly-effect, we morph to a scene of Walter; he's bearded, disheveled, urine-stains on his trousers. He's in his room at St. Clair's, and the walls around him are filled with all types of strange diagrams and equations. It's the ravings of a mad-man, scribbled on the wall. A gravelly voice calls his name and as Walter turns, we see it's William Bell.

Bell: "Walter, you must realize this is all in your mind. None of this actually happened."

Walter: "But it did! Peter was taken to the Other Side and we went to rescue him! And you were there too, Belly! You were living in the Twin Towers and then you were a cartoon! And Nina was really old and in a wheelchair. It happened, all if it, I tell you!"